1. Field of the Invention
The invention is aimed at easily adjustable bicycle frame for change in the riding modes. More specifically to such an adjustable bicycle frame allows a rider to incrementally adjust length between front wheel and rear, and a length between seat tube and head tube which coherently change inclined angles of both the seat tube and the head tube in an attempt to attain a selected riding mode for the rider while accepting riders of different body height.
2. Description of Related Art
A conventional bicycle comprises a bottom bracket in which component of a crank with two pedals are secured, a seat tube joins the bottom bracket and extending upward out of it, a chain stay also joins both the bottom bracket and the seat tube and extending rearward out of it. A head tube with a fork pivotably secured to the head tube and extending downward, and a down tube and a crossbar interconnecting the head tube and the seat tube. Other bicycle components are comprised of a rear wheel rotatably secured to the chain stay, a front wheel rotatably secured to the fork stay, a seat post partially fastened to the seat tube, a saddle mounted on the seat post, a stem secured to the head tube, a handlebar secured to the stem for allowing a rider to steer the handlebars in conducting the bicycle, a pedal powered transmission which convey the power to both wheelers and a brake device.
The size and inclined angels of bicycle frame can be configured to accept individuals of different ages and body heights (e.g. bicycles for children, bicycles for teenagers, and bicycles for adults) as well as riding modes (e.g. racing mode, urban mode, and all terrain mode). Fork and head tube are coaxial, hence they have the same inclined angle. In the following description, an inclined angle of the head tube is equal to that of the fork if not described otherwise. The inclined angle of a part stands for an angle of the part with respect to the ground. These are described in the following examples:
As bicycles for children, teenagers, and adults, they are different not only in wheel diameter but also the length between two wheels, front and rear. In general, crossbar and the length between front wheel and rear wheel are shorter for children's and teenager's bicycles, while crossbar and the length between front wheel and rear wheel are longer for adult's bicycles so as to accept tall riders.
Performance of a bicycle relies on the sizes and angles of those parts configured in the bicycle frame. Small changes in terms of the sizes and angles of the parts of bicycle frame will put great impacts on the performance of a bicycle certainly it affects a rider's performance. Since racing bicycles and all terrain bicycles are designed to be greater inclined angles of seat tube and head tube, therefore appropriate for high speed riding. A greater inclined angle (i.e., in the range of 73-75 degrees) is required for seat tube of racing bicycle in order to boost pedaling efficiency. Also, a greater inclined angle (i.e., in the range of 73-75 degrees) are required for head tube for the racing bicycle so as to increase maneuverability. Further, an increased length between seat tube and handlebars is required too. Thus, a rider might lean himself forward in an attempt to minimize drag and boost pedaling efficiency. However, style of riding as leaning forward may be appropriate for professionals but not suitable for ordinary riders who may tend to susceptible to be tiresome. Hence, such angle are not appropriate for slow and relaxed urban riding.
The “city bike” among various bicycles of different utility, is given smaller inclined angles of seat tube and head tube to facilitate for low speed urban riding. The “city bikes” are characterized by relaxed, therefore tend to use shorter length between seat tube and handbar. It is commonly known fact that the inclined angle (i.e., in the range of 69-71 degrees) is typical for seat tube and head tube of the bicycle for city. The smaller inclined angles of seat tube and head tube may hinder pedaling. But it can decrease vibration from the ground when riding. Thus, it is a little merits of comfort. However, there are some drawbacks as well, bicycles having smaller inclined angles of seat tube and head tube are proved not to be appropriate for both high speed riding and hill climbing.
The length between seat tube and head tube is defined as the crossbar length and it should be varied in accordance with the rider's body heights. Longer crossbar length is appropriate for tall persons with longer arms and legs. Further, crossbar length and inclined angles of both head tube and seat tube of a certain riding mode should be slightly different from those another riding mode. An increased length between front wheel and rear wheel, in other words, longer crossbar is required for racing mode. This is because it enables a rider to become forward-leaning pose in order to decrease drag. What's more, greater inclined angle of the seat tube can boost pedaling efficiency. Bicycles with shorter crossbar length are appropriate for relaxed urban riding. Rider may sit upright easily to enjoy riding. It was found that smaller inclined angles of both the head tube and the seat tube help to minimize vibration picked up from the ground.
It is understood through the analysis given above, parts of bicycle frame and inclined angels of the parts should be configured to be able to accept individuals of different ages with body heights yet even their riding modes preferred. (e.g., racing mode, urban mode, and all terrain mode). Normally, frames of typical bicycles are fixed while manufacture. Therefore, it is impossible for the user to change sizes and geometry of the frame. That is, there is no choice, the rider will end up in no choice of selecting an appropriate one. Thus, for a rider could be injured and may be serious at times after a prolonged period of riding. This could be frustrating factor for an enthusiastic rider. Normally, it is impossible of reconfiguring bicycle parts for changing length between two parts and inclined angles of the parts of a typical bicycle frame in order to accommodate different riding modes and different riding conditions.
China Patent Numbers ZL02116476.2 and ZL03264805.7 both disclose a telescopic bicycle and they are characterized in that the crossbar is made telescopic so that the occupying space of a bicycle can be decreased in storage. The length between front wheel and rear wheel are adjustable to suit different heights of the rider. But a sliding tube of the telescopic crossbar may extend to pass the seat tube in the adjustment. To avoid conflicting with the rear wheel space, the telescopic crossbar is placed horizontally above the rear wheel. Inclined angle of the head tube is about the same as that of the seat tube when adjusting the telescopic crossbar. It is impossible of coherently change inclined angles of the head tube and the seat tube while decreasing the length between the head tube and the seat tube. Thus, center of the bicycle is shifted forward in riding after shortening the telescopic bar. And in turn, a rider may tend to tip when descending a hill. What's more, its stability is downgraded.
There is another telescopic bicycle which is characterized in that the crossbar horizontally interconnecting the seat tube and the head tube is cut into two telescopic pieces each having one end secured to the head tube or the seat tube by welding. Further, a lock nut is used to fasten the two pieces together after adjusting length of the crossbar. However, since it can only change length between front wheel and rear wheel and the inclined angles of both seat tube and head tube are still the same, so it cannot implement different riding modes. Thus, center of the bicycle is shifted forward in riding after shortening the telescopic bar. And in turn, a rider may tend to tip when descending a hill. What's more, its stability is downgraded. What's worse, the rider may face the risk of falling off.